It is going to depend on your goals. Are you looking at buying vintage cards strictly as an investment and/or for flipping VS collecting players/cards you like which hopefully will appreciate in value over time?
I have been buying/selling almost exclusively vintage cards for 30+ years and the biggest difference (Outside of the past 18 months) is that vintage material rarely is something you buy and flip 2 weeks later for a big markup. Prices of quality material tend to increase over time, but it sometimes can take years to see significant changes. I always suggest that people identify a few players they like and then some cards for each of those players you want. Do your research to see what the market is on those cards and then start shopping. I personally stick to graded cards for most anything I buy as an investment as they just way easier to resell, tend to have a better ROI vs raw and have a significantly lower risk of altered/fake cards. Unfortunately most shops and smaller shows offer a very limited selection of vintage material so you will likely have to look online or go to a larger show to find things you want. Buying raw vintage off ebay or some user group can be a real shoot as most people don't grade properly (Some on purpose, some from lack of knowledge) I would say start small and see how you like what you buy before buying anything more expensive.
Feel free to use my website as a reference tool on vintage material and shoot me any q's you have.
Tim Payne
PayneSportsCollectibles.com